Sam Miller of the Orange County Register has an outstanding post up that looks at the Baseball American Top 100 prospect list heading into the 2001 season, and compares it to what the top 100 players in the minor leagues at that time have turned out to be (so far), in terms of WAR.
It is really fascinating to go through the list and see not only the guys who, at that time, were can't miss and did miss (4 of the top 10 at the time -- Corey Patterson, Sean Burroughs, Jon Rauch, and Ryan Anderson -- don't make the actual top 100 performers), but take a look at how few players there are who go on to really great careers that are in the minors at any given time.
The list of the top 100 performers since 2001* includes players like Damaso Marte, Ryan Ludwick, Brian Schneider, Justin Duchscherer, Omar Infante, Scott Podsednik, and Brian Fuentes. Basically, if you have two-three good years as a regular, or hang around for six to eight years as a role player, you're going to be one of the 100 best players in the class.
* Ten years later is, of course, early for evaluating an entire career, and this list would probably look different in five years or so, as more players who were in their teens in February, 2001, and who are now in their late 20s add to their value.
Miller also goes through and compares the top five prospects from BA's rankings for each team to the actual five best players in each team's minor league system.
This is really great research and work by Miller, and well worth everyone here taking a look at.